I took my car in for a metallic rattling in the driver's door, which was aggravated by bass from the speaker. They said they 'tightened some bolts' but did absolutely nothing.

I ended up having to take the door panel off myself. It was kind of a pain in the ass and I never figured out how to disconnect one of the wiring harness clips... but a small metal tab fell out in the process. Didn't seem to come from anywhere so I figure it's just an accidental extra. Solved the problem.